Actually the examples we discuss here are simple, but in your website things will get complicated. We will study real-world examples later in the series. You need a way to remember why you have used a coloring technique over others. You can use CSS Comments syntax to comment in your code and add notes. It's a very useful thing to do because maybe you will come back after 2 years to update your style sheet, and you will need your comments to know what you have done. I have commented the above colors example as following

body
{
  font-family: Tahoma;
}
/* This is the red color RGB value */
.TheRed
{
  color: rgb(100%,0%,0%);
}
/* This is the green color RGB value */
.TheGreen
{
  color: rgb(0%,100%,0%);
}
/* This is the blue color RGB value */
.TheBlue
{
  color: rgb(0%,0%,100%);
}
/* This is the yellow color RGB value */
.TheYellow
{
  color: rgb(100%,100%,0%);
}
/* This is the cyan color RGB value */
.TheCyan
{
  color: rgb(0%,100%,100%);
}
/* This is the magenta color RGB value */
.TheMagenta
{
  color: rgb(100%,0%,100%);
}
/* This is the black color RGB value */
.TheBlack
{
  color: rgb(0%,0%,0%);
}